The invention relates to antimicrobial polymers obtained by polymerizing acryloxyalkylamines. The invention further relates to a process for preparing these antimicrobial polymers and to their use.
It is highly undesirable for bacteria to become established or to spread on the surfaces of piping, or of containers or packaging. Slime layers frequently form and permit sharp rises in microbial populations, and these can lead to persistent impairment of the quality of water, drinks or foods, and even to spoilage of the product and harm to the health of consumers.
Bacteria must be kept away from all fields of life where hygiene is important. This affects textiles for direct body contact, especially in the genital area, and those for the care of the elderly or sick. Bacteria must also be kept away from surfaces of the furniture and equipment used in patient-care areas, especially in areas for intensive care or neonatal care, and in hospitals, especially in the areas where medical intervention takes place, and in isolation wards for critical cases of infection, and also in toilets.
A current method of treating equipment, or the surfaces of furniture or of textiles, to resist bacteria either when this becomes necessary or else as a precautionary measure, is to use chemicals or solutions or mixtures of these which are disinfectants and therefore have fairly broad general antimicrobial action. Chemical agents of this type act nonspecifically and are frequently themselves toxic or irritant, or form degradation products which are hazardous to health. In addition, people frequently exhibit intolerance to these materials once they have become sensitized.
Another method of counteracting surface spread of bacteria is to incorporate substances with antimicrobial action into a matrix.
U.S. Pat. No. 4,532,269, for example, discloses a terpolymer made from butyl methacrylate, tributyltin methacrylate, and tert-butylaminoethyl methacrylate. This copolymer is used as an antimicrobial paint for ships, and the hydrophilic tert-butylaminoethyl methacrylate present promotes gradual erosion of the polymer and thus releases the highly toxic tributyltin methacrylate, which is the antimicrobial active ingredient.
In these applications, the copolymer prepared with aminomethacrylates is merely a matrix or carrier for added microbicidal ingredients which can diffuse or migrate out of the carrier material. Sooner or later, polymers of this type loose their activity, once the necessary minimum inhibitor concentration (MIC) at the surface has been lost.
The European patent application 0 862 858 has also disclosed that copolymers of tert-butylaminoethyl methacrylate, a methacrylate with a secondary amino function, has inherent microbicidal properties. Systems developed in the future will again have to be based on novel compositions with improved effectiveness if undesirable resistance phenomena in the microbes are to be avoided, particularly bearing in mind the microbial resistance known from antibiotics research.
The object on which the present invention was based was therefore to develop novel antimicrobial polymers. When used as a coating or covering material, these should prevent bacteria from colonizing surfaces and spreading thereon.
Surprisingly, it has now been found that homopolymerization of acryloxyalkylamines or of methacryloxyalkylamines gives polymers which are lastingly microbicidal, are not damaged by solvents or physical stresses, and exhibit no migration. There is no need here for the use of other biocidal active ingredients. The surface of the polymers is, of course, important for the antimicrobial action of these homopolymers.
The present invention therefore provides antimicrobial polymers which are obtained by polymerizing a monomer of the formula I: 
where
R1=xe2x80x94H or xe2x80x94CH3 
R2=branched or unbranched aliphatic hydrocarbon radical having from 1 to 5 carbon atoms,
R3=H, or branched or unbranched aliphatic hydrocarbon radical having from 1 to 7 carbon atoms,
R4=H, or branched or unbranched aliphatic hydrocarbon radical having from 1 to 7 carbon atoms,
R5=H, or branched or unbranched aliphatic hydrocarbon radical having from 1 to 7 carbon atoms, and
X=O, NH, NR5.
Acryloyloxyalkylamines (X=0) and alkylaminoacryl-amides (X=NH) are particularly suitable for preparing the polymers of the invention.
The radicals R3 and R4 may be identical or different. If R3 and/or R4 are hydrocarbon groups, these may in particular be methyl, ethyl, isopropyl, n-propyl, or tert-butyl groups.
Preferred monomers used of the formula I are 2-tert-butylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, 2-dimethylaminomethyl methacrylate, 2-tert-butylaminoethyl acrylate, 3-dimethylaminopropyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethyl-aminoethyl acrylate, N-3-dimethylaminopropylmeth-acrylamide, N-3-diethylaminopropylmethacrylamide, N-3-dimethylaminopropylacrylamide, or N-3-diethylamino-propylacrylamide.
The antimicrobial polymers of the invention may be obtained by homopolymerizing monomers of the formula I. The free-radical polymerization advantageously takes place by a chemical route by way of a free-radical initiator, or initiated by radiation. The examples describe typical procedures.
The present invention further provides antimicrobial polymer blends which are prepared by mixing one or more antimicrobial polymers each obtainable by polymerizing monomers of the formula I, where R1, R2, R3, R4, R5 and X are as defined above, with at least one other polymer.
Examples of blend material, i.e. other polymer with which the polymer of the invention is mixed, are polyurethanes, PVC, polyolefins, such as polyethylene or polypropylene, polysiloxanes, polystyrenes, polyacrylates, polymethacrylates, and engineering plastics, e.g. polyamides or polyterephthalates. To obtain adequate antimicrobial action of a polymer blend, the proportion of the antimicrobial polymer of the invention should be from 0.2 to 90% by weight, preferably from 40-90% by weight.
In principle, any of the processes known in the art, for example as described in detail by H.-G. Elias, MakromolekUle [Macromolecules], Vol. 2, 5th edition, pp. 620 et seq., may be used to prepare the antimicrobial polymer blends. For example, two previously formed polymers are mixed in the melt by mixing the pelletized or pulverulent polymers on roll mills, in kneaders, or using extruders. In the case of thermoplastics, this is achieved by heating above the glass transition temperatures or melting points. In the case of solution mixing, the starting materials are separately prepared solutions of the two polymers in the same solvent.
In specific embodiments of the present invention, it is possible for the proportion of the one or more antimicrobial polymers of the invention in a blend to be less than 40-90% by weight, e.g. from 0.2 to 70% by weight, preferably from 0.2 to 30% by weight, particularly preferably from 0.2 to 15% by weight, very particularly preferably from 0.2 to 10% by weight.
One preferred process for preparing the antimicrobial polymers and, respectively, polymer blends of the invention is free-radical polymerization of monomers of the formula I in solution, using a free-radical initiator. The resultant antimicrobial polymers may, where appropriate after mixing with other polymers, be applied to a surface by known methods, such as dipping, spraying, or spreading. Solvents which have proven successful are ethanol, methanol, water/alcohol mixtures, methyl ethyl ketone, diethyl ether, dioxane, hexane, heptane, benzene, toluene, chloroform, dichloromethane, tetrahydrofuran, and acetonitrile, but it is also possible to use other solvents as long as they have sufficient capability for dissolving the polymers and give good wetting of the substrate surfaces. Solutions with polymer contents of from 3 to 20% by weight, for example about 5% by weight, have proven successful in practice and generally give, in a single pass, coherent coatings which cover the substrate surface and may have a thickness of more than 0. 1 xcexcm.
It is also possible for the antimicrobial polymers and, respectively, polymer blends of the invention to be in the form of a melt when applied to the substrates, e.g. by coextrusion, or by way of dipping, spraying, or surface-coating.
The antimicrobial polymers and, respectively, polymers blends of the invention may moreover also be used as additives or components for formulating polymer blends, inks or paints, surface coatings, or biocides.
In the case of the polymer blends, a particularly advantageous method is compounding by way of extrusion, where appropriate also by way of coextrusion with other polymers.
If polymers or, respectively, polymer blends of the invention are used as an additive or component in inks or paints, surface coatings, or biocides, much lower concentrations may be sufficient, e.g. in the range of a few parts per hundred or per thousand.
The present invention further provides the use of the antimicrobial polymers and, respectively, polymer blends of the invention for producing antimicrobial products, and the resultant products per se. The products may comprise antimicrobial polymers of the invention or consist of these. Products of this type are preferably based on polyamides, on polyurethanes, on polyether block amides, on polyesteramides or -imides, on PVC, on polyolefins, on silicones, on polysiloxanes, on polymethacrylate, or on polyterephthalates, which have surfaces coated with polymers of the invention or have been processed using polymers of the invention, in the form of a polymer blend.
Examples of antimicrobial products of this type are machine parts for processing food and drink, components in air conditioning systems, roofing, items for bathroom and toilet use, kitchen items, components for sanitary installations, components of animal cages or of animal houses, recreational products for children, components of water systems, packaging for food or drink, operator units (touch panels) of devices, and contact lenses.
The polymers and, respectively, polymer blends of the invention may be used anywhere where importance is placed on surfaces which are as free as possible from bacteria, i.e. are microbicidal, or on surfaces with release properties. Examples of applications of the polymers and, respectively, polymer blends of the invention are in particular surface coatings, protective paints, and other coatings in the following sectors:
marine: boat hulls, docks, buoys, drilling platforms, ballast water tanks
construction: roofing, basements, walls, facades, greenhouses, sun protection, garden fencing, wood protection, tent roof material, fabrics
sanitary: public conveniences, bathrooms, shower curtains, toilet items, swimming pools, saunas, jointing, sealing compounds
requisites for daily life: machines, kitchen, kitchen items, sponge pads, recreational products for children, packaging for food or drink, milk processing, drinking water systems, cosmetics
machine parts: air conditioning systems, ion exchangers, process water, solar-powered units, heat exchangers, bioreactors, membranes
medical technology: contact lenses, diapers, membranes, implants
consumer articles: automobile seats, clothing (socks, sports clothing), hospital equipment, door handles, telephone handsets, public conveyances, animal cages, cash registers, carpeting, wallpapers.
The polymers and, respectively, polymer blends may likewise be used as an additive for surface coatings in the maritime sector, in particular for eliminating larval barnacles on boat hulls, and generally as an additive in antifouling paints, particularly in sea water in which salt is present.
The antimicrobial polymers and, respectively, polymer blends of the invention may also be used as additives in formulating cosmetic products, e.g. for pastes or ointments. Here the proportion of polymers or, respectively, polymer blends of the invention may be lowered as fat as relatively small numbers of parts per hundred or parts per thousand, depending on the activity of the polymer and the formulation.
The polymers and, respectively, polymer blends of the invention are also used as a biofouling inhibitor in cooling circuits. To prevent damage to cooling circuits by infestation with algae or bacteria, the circuits would have to be cleaned frequently or appropriately oversized. In open cooling systems, as are usually found in power plants and in chemical plants, the addition of microbicidal substances such as formalin is not possible. Other microbicidal substances are frequently highly corrosive or form foams, preventing their use in systems of this type.
In contrast, the inventive polymers or blends of these with the other polymers mentioned may be fed in finely dispersed form into the process water. The bacteria are killed on contact with the antimicrobial polymers and, if necessary, removed from the system by filtering off the dispersed polymer/blend. Deposits of bacteria or algae on sections of the plant can thus effectively be prevented. The result of this is a completely novel process for eliminating or reducing biofouling in process water systems.
The present invention therefore also provides processes for sterilizing cooling water streams, by adding antimicrobial polymers or polymer blends of these in dispersed form to the cooling water. For the purposes of the present invention, cooling water includes any process water stream which is used for heating or cooling purposes in closed or open circulating systems.
The dispersed form of the copolymers or of their blends may be obtained within the preparation process itself, for example by emulsion polymerization, precipitation polymerization, or suspension polymerization, or subsequently by comminuting, e.g. in a jet mill. The size distribution of the resultant particles when they are used is preferably from 0.001 to 3 mm (diameter of particles), firstly providing a large surface for killing the bacteria or algae and secondly enabling, if required, ready separation from the cooling water, e.g. by filtration. One way of working the process is to remove from the system continuously a proportion (5 to 10%) of the copolymers/blends used and to replace it with an appropriate amount of fresh material. As an alternative, the number of microbes in the water may be checked, and further antimicrobial copolymer/blend added as required. Depending on the quality of the water, it is sufficient to use from 0.1 to 100 g of antimicrobial copolymer or blends of these per m3 of cooling water.
The present invention also provides the use for producing hygiene products or items for medical technology, of the polymer substrates modified on the surface using polymers or, respectively, polymer blends of the invention. The statements above concerning preferred materials are again applicable. Examples of hygiene products of this type are toothbrushes, toilet seats, combs, and packaging materials. For the purposes of the present invention, hygiene items also include articles which can come into contact with many people, for example telephone handsets, stair rails, door handles, window catches, and also grab straps and grab handles in public conveyances. Examples of items for medical technology are catheters, tubing, protective or backing films, and also surgical instruments.
The uses mentioned for the antimicrobial polymers also apply to the polymer blends of the invention.
The examples below are given for further description of the present invention, but are not intended to limit the scope of the invention as set out in the claims.